Run `mvn clean install` to build all sample programs

Sample program consuming high CPU usage

A java program consuming high CPU usage. This program was inspired by a sample found in the article "[Identifying which Java Thread is consuming most CPU](http://code.nomad-labs.com/2010/11/18/identifying-which-java-thread-is-consuming-most-cpu/)"

Sample to show hot methods in Java Flight Recording

This program checks whether a given random number is primitive or not.

Run the program without any arguments and also make a profiling recording.

For example:

In Code -> Hot Methods tab, you should see that the program has spent a lot of time in the LinkedList.indexOf(Object) method, which is called from contains method.

By changing LinkedList to a HashSet, you can make the program run a lot faster.

The contains methods in Linked List checks all the items. Algorithm run time is O(n). However the HashSet contains algorithm's run time is O(1).

Check the runtime using HashSet.

Use `time` command in Linux to measure the time.

<?xml version="1.0" encoding="utf-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

<parent>

<groupId>com.github.chrishantha.sample</groupId>

<artifactId>java-samples</artifactId>

<version>0.0.2-SNAPSHOT</version>

<relativePath>../pom.xml</relativePath>

</parent>

<modelVersion>4.0.0</modelVersion>

<artifactId>hotmethods</artifactId>

<packaging>jar</packaging>

<name>hotmethods</name>

<dependencies>

<dependency>

<groupId>com.beust</groupId>

<artifactId>jcommander</artifactId>

</dependency>

</dependencies>

<properties>

<fully.qualified.main.class>com.github.chrishantha.sample.hotmethods.App</fully.qualified.main.class>

</properties>

</project>

package com.github.chrishantha.sample.hotmethods;

import com.beust.jcommander.JCommander;

import com.beust.jcommander.Parameter;

import java.util.Collection;

import java.util.HashSet;

import java.util.LinkedList;

import java.util.Random;

public class App {

@Parameter(names = "--count", description = "Random Numbers Count")

private int randomNumbersCount = 1000000;

@Parameter(names = "--max", description = "Maximum limit to generate prime numbers")

private int max = 100000;

@Parameter(names = "--use-set", description = "Use Hash Set for Prime Numbers", arity = 0)

private boolean useSet;

@Parameter(names = "--help", description = "Display Help", help = true)

private boolean help;

public static void main(String[] args) {

App app = new App();

final JCommander jcmdr = new JCommander(app);

jcmdr.setProgramName(App.class.getSimpleName());

jcmdr.parse(args);

System.out.println(app);

if (app.help) {

jcmdr.usage();

return;

}

app.start();

}

private void start() {

Collection<Integer> primeNumbers = useSet ? new HashSet<>() : new LinkedList<>();

System.out.println("Generating Prime numbers between 1 and " + max);

for (int i = 1; i < max; i++) {

boolean isPrimeNumber = true;

// Check whether the number is prime

for (int j = 2; j < i; j++) {

if (i % j == 0) {

isPrimeNumber = false;

break;

}

}

if (isPrimeNumber) {

primeNumbers.add(i);

}

}

Random random = new Random();

System.out.println("Checking Random Prime numbers");

int count = 0;

for (int i = 1; i < randomNumbersCount; i++) {

int randomNumber = random.nextInt(max);

if (primeNumbers.contains(randomNumber)) {

count++;

}

}

System.out.format("Found %d prime numbers from %d random numbers%n", count, randomNumbersCount);

}

@Override

public String toString() {

StringBuilder builder = new StringBuilder();

builder.append("App [randomNumbersCount=");

builder.append(randomNumbersCount);

builder.append(", max=");

builder.append(max);

builder.append(", useSet=");

builder.append(useSet);

builder.append("]");

return builder.toString();

}

}

Sample to show latencies in Java Flight Recording

This program has two threads: Even and Odd to print Even and Odd numbers.

Run the program without any arguments and also make a profiling recording.

For example:

In Threads -> Latencies tab, you should see that the program has many blocked events.

You should also see red blocks in Events -> Graph tab. Red blocks are not good as the thread is just waiting to acquire a lock.

See Threads -> Contention tab to see the Locks and also see Threads -> Lock Instances to check whether both threads share the same lock instances.

Since there is no shared resource, you can avoid the lock and improve the performance.

Run the program without locks.

<?xml version="1.0" encoding="utf-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

<parent>

<groupId>com.github.chrishantha.sample</groupId>

<artifactId>java-samples</artifactId>

<version>0.0.2-SNAPSHOT</version>

<relativePath>../pom.xml</relativePath>

</parent>

<modelVersion>4.0.0</modelVersion>

<artifactId>latencies</artifactId>

<packaging>jar</packaging>

<name>latencies</name>

<dependencies>

<dependency>

<groupId>com.beust</groupId>

<artifactId>jcommander</artifactId>

</dependency>

</dependencies>

<properties>

<fully.qualified.main.class>com.github.chrishantha.sample.latencies.App</fully.qualified.main.class>

</properties>

</project>

package com.github.chrishantha.sample.latencies;

import com.beust.jcommander.JCommander;

import com.beust.jcommander.Parameter;

public class App {

@Parameter(names = "--count", description = "Print Count")

private int count = 50;

@Parameter(names = "--lock", description = "Lock", arity = 1)

private boolean lock = true;

@Parameter(names = "--help", description = "Display Help", help = true)

private boolean help;

public static void main(String[] args) {

App app = new App();

final JCommander jcmdr = new JCommander(app);

jcmdr.setProgramName(App.class.getSimpleName());

jcmdr.parse(args);

System.out.println(app);

if (app.help) {

jcmdr.usage();

return;

}

app.start();

}

private class EvenThread extends Thread {

public EvenThread() {

super("Even-Thread");

}

@Override

public void run() {

for (int i = 0; i < count; i++) {

printEven(i);

}

}

}

private class OddThread extends Thread {

public OddThread() {

super("Odd-Thread");

}

@Override

public void run() {

for (int i = 0; i < count; i++) {

printOdd(i);

}

}

}

private void printNumber(int i) {

System.out.format("Thread: %s, Number: %d%n", Thread.currentThread().getName(), i);

}

private void printEven(int i) {

if ((lock && isEvenLocked(i)) || isEven(i)) {

printNumber(i);

}

}

private void printOdd(int i) {

if ((lock && !isEvenLocked(i)) || !isEven(i)) {

printNumber(i);

}

}

private synchronized boolean isEvenLocked(int i) {

return isEven(i);

}

private boolean isEven(int i) {

try {

Thread.sleep(1000);

} catch (InterruptedException e) {

e.printStackTrace();

}

return i % 2 == 0;

}

private void start() {

new OddThread().start();

new EvenThread().start();

}

@Override

public String toString() {

StringBuilder builder = new StringBuilder();

builder.append("App [count=");

builder.append(count);

builder.append("]");

return builder.toString();

}

}